In a transfer lamination process or method, a transfer device or unit is used to transfer an overlaminate material from a transfer ribbon to a surface of a substrate through the application of heat and pressure. This process can be used to provide protection to the surface from abrasion and environmental conditions, for example. When the overlaminate material contains an image, the transfer lamination process can be used to transfer the image to the surface of the substrate.
The overlaminate material transferred to the surface of the card substrate using the heated roller is generally one of two types: a patch laminate, or a fracturable laminate or transfer layer often referred to as a “thin film laminate.” The patch laminate is generally a pre-cut polyester film that has been coated with a thermal adhesive on one side. The pre-cut patch is removably attached to a continuous carrier web. The transfer unit heats the patch to activate the adhesive and presses the adhesive-coated side of the patch to the surface of the substrate to bond the patch to the surface. The carrier web is detached from the patch to complete the transfer operation.
Transfer layers or films are generally continuous resinous materials that have been coated onto a continuous carrier web or backing. The side of the resin material that is not attached to the continuous carrier web is generally coated with a thermal adhesive. The transfer unit is used to activate the adhesive and press the adhesive-coated resinous material against the surface of the substrate to bond the material to the surface. The carrier web or backing is then removed to complete the transfer lamination process.
Credential production devices often include transfer units to perform a transfer lamination process on credential substrates to form the desired credential product. Exemplary credentials include identification cards, driver's licenses, passports, and other documents. The credential substrates, on which the transfer lamination process is performed, typically include card substrates formed of plastic or other material.
One disadvantage to the use of a patch laminate with a credential card substrate is that the patch laminate does not provide full edge-to-edge protection to the surface of the card substrate. This is because the patch laminate must be formed slightly smaller than the surface of the card substrate to ensure that the patch laminate does not extend beyond the edges of the substrate.
One advantage of the use of a transfer film is that it can be laminated over the entire surface of a credential card substrate. After the transfer unit bonds the transfer film to the surface of the card substrate, the transfer film fractures along the edges of the substrate as the web carrier is removed from the bonded portion of the transfer film. Thus, the transfer film can provide full edge-to-edge coverage of the surface of the card substrate. As a result, transfer films can provide greater surface protection than patch laminates.
Transfer units of credential production devices utilize the transfer film as a print intermediate to form an image on the credential card substrate in accordance with a reverse-image printing process. In the reverse-image printing process, an image is printed to the exposed side of the transfer film prior to its lamination to the surface of the card substrate. Next, the image on the transfer film is registered with the card substrate. The transfer unit is used to activate the adhesive on the imaged transfer film causing the imaged transfer film to bond to the surface of the card substrate. The carrier web of the transfer ribbon is then removed from the bonded imaged transfer film to complete the transfer of the image to the card substrate. The transfer film provides protection to the image and the surface of the card substrate.
The quality of the image printed in accordance with the above-described reverse-image printing process is partially determined by the tension in the transfer ribbon during the bonding or transfer phase of the process. Too much tension in the transfer ribbon during the transfer phase causes the image to be stretched. Too little tension in the transfer ribbon during the transfer phase may cause wrinkling of the transfer ribbon and undesirable creases in the bonded image. Accordingly, it is important to control the amount of tension in the transfer ribbon during the transfer phase.
Some transfer films include a protective layer that is configured to provide protection to the surface of the substrate to which the transfer layer is adhered. This also provides protection to any image printed on the transfer layer or printed on the surface of the substrate. In general, the protective layer provides abrasion resistance, but can also provide protection from other environmental conditions, such as moisture, ultraviolet light, and other conditions.
Edge flash occurs when the transfer film does not fracture properly along an edge of the substrate, such as the trailing edge, during the web carrier release or peeling phase of the transfer lamination process. This results in portions of the transfer film remaining adhered to the carrier web or the substrate that were respectively intended to bond to the substrate or the carrier web during the transfer lamination process. One cause of such flash is improper tension in the transfer film during the web carrier peeling phase of the transfer lamination process.